The present invention relates to a system and technique for rehabilitating underground conduits, such as storm and wastewater sewers. More particularly, though not exclusively, the invention relates to an in situ spray lining system for rehabilitating the sewer pipe without needing to establish an above grade external bypass to carry the sewage flow during the rehabilitation process. Instead, the present invention utilizes an internal bypass.
The wastewater infrastructure in the United States is in poor condition. The American Society of Civil Engineers 2017 Infrastructure Report Card reviewed the condition of the existing wastewater infrastructure and issued a “D+” grade score. Critical sewer interceptors in many of the nation's older communities are 100 years old. The cost of replacing this century old infrastructure is significant, and the physical replacement is often not practical due to multiple decades of development around and often above these key assets. As a result, there has long been a considerable need for rehabilitation technologies that can extend the useful life of existing sewer assets while minimizing project cost and community disruption.
However, most rehabilitation processes are not designed to be performed on an active sewer, and thus, the sewer needs to be taken off-line during the rehabilitation process. This is typically accomplished by setting up a temporary external bypass to carry the sewage around the section that is being rehabbed during the duration of the rehabilitation project. Once the sewer is off-line, the inner wall of the sewer pipe is cleaned and inspected, and then ultimately rehabilitated.
Typically, an above grade external bypass is constructed to allow for the cleaning, inspection and rehabilitation of the sewer pipe. Utilizing an above grade external bypass method typically represents approximately 10% to 20% of the total rehabilitation project costs and adds an additional 4 to 10 weeks to the total rehabilitation project time schedule.
The above grade external bypass method requires appropriate local or state authorized permitting for work in the right-of-way. It requires agreements with property owners whose property is impacted. It causes general disruption when roads, driveways and sidewalks need to be blocked for the duration of the project. It often requires placement of above grade piping across railroad tracks, major roadways, waterways and private property, making the above grade external bypass method expensive and at times functionally impractical.
The above grade external bypass method requires additional authorized permitting to work in any environmentally sensitive areas such as parks, rivers, creek beds, etc. Moreover, there is environmental risk with an above grade external bypass as raw sewage is being pumped above ground where an accident or vandalism may result in a harmful release.
The above grade external bypass method requires coordination of the bypass pumping subcontractor schedules, set-up time, testing, and teardown time. This lengthens the overall rehabilitation project schedule and increases the risk of project delay.
Furthermore, it is challenging to create an accurate sewer rehabilitation project timeline because the visibility to the inner wall of the sewer pipe is not accessible until the above grade external bypass is in place and operational. Only after gaining visibility to the entire inner wall of the sewer pipe, can a complete assessment of the defective sewer pipe be made. At that point, the length of time the above grade external bypass must remain in place is estimated, and the associated disruptions and costs can sometimes increase exponentially.
The above grade external bypass methodology results in increased project cost, disruption to residents, businesses and commuters, heightened permitting requirements, longer project timeframes and increased environmental risk. By utilizing an internal bypass methodology, the sewer rehabilitation can be performed without the additional costs, risks, delays and disruptions associated with utilizing an above grade external bypass.
Use of this internal bypass methodology increases the rate at which sewers can be rehabilitated and reduces the overall costs to property owners, ratepayers, communities and government agencies. By eliminating the significant disruption and expense of an above grade external bypass, many more sewer rehabilitation projects may be completed that otherwise would not have even been attempted. Furthermore, rehabilitation that is currently performed with an internal bypass (sewers approximately 48 inches in diameter or greater utilizing physical manned entry and manual hand spray of rehabilitation material) would increase in cost effectiveness, safety and quality with the utilization of this internal bypass methodology.
Moreover, there have been important advancements in rehabilitation technologies. Long-term studies (i.e. “Evaluation of Protective Coatings for Concrete” performed by County Sanitation Districts of Los Angeles County, Whittier, Calif., December 2004) have documented the performance of a wide array of technologies over long-term controlled exposure to corrosive sewer conditions. While cured in place pipe (CIPP) lining is currently the preferred rehabilitation technology for many communities, there are now many spray applied rehabilitation materials in the industry with numerous documented successful case studies. Utilizing current methods of application (internal or above grade external bypass), these rehabilitation materials are competitive with existing rehabilitation technologies. They are being bid as a competitive alternative to CIPP, particularly for larger diameter projects.
Prior art established the materials utilized in rehabilitation and the method of pumping and spraying the rehabilitation product at a controlled rate.